Technical Field
The present invention relates to magnetoresistive random access memory (MRAM) and, in particular, to improved patterning techniques for the fabrication of MRAM.
Description of the Related Art
Spin-transfer torque magnetoresistive random access memory (STT-MRAM) devices offer many benefits over semiconductor-based memories such as dynamic RAM (DRAM) and static RAM (SRAM). However, patterning MRAM devices at the small sizes (e.g., <50 nm), large densities (>1 Gb/cm2), and high uniformity (e.g., <±3 nm) needed to compete with DRAM and SRAM is difficult. Two of the most difficult-to-solve problems encountered are poor uniformity across large arrays and low yield of devices smaller than 50 nm. Existing fabrication techniques produce devices that vary significantly in their size and electrical properties, often producing devices that are non-functional or are outside of design parameters. As a result, many devices that are formed for memory arrays are not suitable for the task.
STT-MRAM is a non-volatile memory technology that uses spin-aligned electrons to transfer torque to magnetic domains of the memory device. The torque delivered to the magnetic domain changes the amount of current needed to change the magnetic state of a cell.
Conventional methods of forming MRAM devices use positive-tone resist developer and a positive resist with a bright-field reticle to form the MRAM stack. However, these methods suffer from a lack of roundness and uniformity in their critical dimensions.